Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to high pressure metal vapor
lamps and more specifically high pressur~ sodium vapor lamp~
utilizing alu~ina ceramic envelopes~ The invention is parti-
cularly concernad with means to facilitate the ~tarting of
such lamps.
High intensity sodium vapor lamp8 of the pre~ent
kind are de~cribed in U.S. Patent No. 3,248,590 - Schmidt,
issued April 26, 1966, entitled "High Pressure Sodium Vapor
LampH. These lamps utilize a slender tubular envelope of
light-transmissive refractory oxide material resistant to
sodium at high temperatures, suitably high den~ity polycry-
stalline alumina or ~ynthetic sapphire. The filling comprisss
~odium along with ~ rare gas to facilitate starting, and mer-
cury for improvod efficiency. The end~ of the alumina tube
are ~ealed by suitable closure members affording connection
to thermionic electrodes which may comprise a re~ractory
metal structure activated by electron emi~ive material.
The ceramic arc tube i8 generally supported within an outer
vitreous envelope or jacket provided at one end with the
usual screw base. The electrod~s of ~he arc tube are connected
to the tsrminal~ of the base, that is to shell and center
contact, and the interenv~lope space i8 usually evacuated in
order to conserve heat.
The high pressure sodium vapor lamps which have
been ~anufactured commercially up to the present time have
gonerally follow~d the te~chings of the Schmidt Patent and
u~ed xenon as the ~tarting gas. The goal has been maximum
e~ficiency and the use of xenon provided an advantage in
efficiency of 10% or mora over the lighter inert gas neon.
The choice of xenon raise~ the ~tarting voltage requirement
and this wa~ met by including in the ballast an el~ctronic
circuit which served ~8 a source of short duration high
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voltage pulses After the lamp is ignited the voltage across
it i~ reduced and a sensing circuit responds thereto and dis-
ables the starting pulse generator
There are advantages to high prossure sodium vapor
lamps which are ea-ier starting than the conventional lamps
oven though they may be lower in efSiciency and the object ~ -
of the inv~ntion is to provido an improved easy starting
lamp of this kind.
It is woll known that easi-r starting of a dis-
eharg- lamp may be achi~ved through the Penning effect call-
ing for a starting gas mixturo comprising major and minor
constitu-nts Penning mixtures are co D nly used in mercury
fluoresc-nt and low pros~ure sodium l mps A suitable P nning
m$xture for a high pressure sodium lamp ~8 a neon-lX argon
mixture With such a starting fill a starting aid in the
form of an internal auxiliary starting eleetrode as sued in
high prossure m~r¢ury vapor lamps or a conduetive stripo
painted on the out-ide of the lamp envelope as used with
fluoresc-nt l mp~ is highly beneficial in furthor reducing the
tarting voltago ~owev r the elosure members or end cap
us-d with ceramic lamp envolopes do not l-nd themselve~ well
to the provision of auxiliary startinq olectrodos Also the
v ry high temporatures of ceramic envelopes may create problems ~ ;
whon conductors are applied or fastoned to tho outsiae.
In accordance with my invention I have re~olved
the problsm by a capac$tive starting aid eomprising a
thermally deformable eonductor whieh rest~ again~t th- out- ;~
side of the arc tube when it i- cold and which is r-tracted
when it is hot
In a pr-ferr d embodiment the ~tarting aid eomprises
a pair of thermally deformablo bimetal arms whose ends embrace
the arc tubo at room temperature to provide a capacitivo ef-
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fect. After the lamp has started and as it beaomes h~atod up
to its normal operating temperature, the bimetal arms swing
away from the arc tube in order to reduce the ob~tru~tion of
light and prevent overheating of the arc tube wall.
I~ the drawing:
FIG. 1 i~ a æide view of a high pr0ssure ~odium
vapor discharga lamp embodying the invention in preferred
form.
FIGS. 2a and 2b are plan section and end elevation
views rospectively of the capacitive starting aid in closed
position.
FIGS. 3a and 3b are corresponding vi~w~ of the
capac~tive starting aid in open position.
FIG. 4 is a plan section of a capacitive tarting
aid which i8 a variant in design.
A high pres~ur~ sodium vapor lamp embodying the
invention in preferred form is illu~trated in FIG. 1. Tho
lamp i8 of approximately 150 watt rating which i~ a relatively
8mall 8ize in which easy starting is particularly de~irable.
The lamp 1 comprise~ an outer envelope 2 o~ glass to the neck
o$ which i8 attached a standard mogul scre~ base 3. The
outer envelope comprises a re-entrant stem press 4 through
which extend, in conventional fashion, a pair of relatively
heavy lead-in conductors 5, 6 whose outer end3 are connected
to the ~c~ew ~hell 7 and eyelet 8 of the ba~e.
The arc tube 9 centrally located within the outer
envelope comprises a length of polycrystalline alumina tubing.
End closures consisting of metal cap~ 10, 11 of niobium which
matche~ the expansion coefficient of alumina ~eramic are seal-
ed to the end~ of the tube by means of a gla~y s-aling ~ompo-
sition. Bnd cap 10 ha~ a metal tube 12 sealed through it
which serves as an exhaust and fill tubulation during
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manufacture of the lamp. The exhaust tube i8 sealed off at
its outer end and serves as a reservoir in which exces~
sodium-mercury amalgam cond0n~es during operation of the lamp,
the illu~trated lamp being intended for base-down operation~
Electrode 13 within the lamp is attached to the inward pro-
jection of exhaust tube 12 and a dummy exhaust tube 14
extending through metal end cap 11 supports the other electrode
15.
Exhaust tube 12 i~ connected by connector 16 and -
short support rod 17 to inlead conductor 6 which provides
circuit continuity from a ba~e terminal to electrode 13. Dum-
my exhaust tube 14 extends through a ring support 18 fastened
to side rod 19 which provides lateral re3traint while allow-
ing axial expansion of the arc tube. A flexible metal strap
20 connects dummy exh~ust tube 14 to side rod 19 which in turn
i8 welded to inlead conductor 5, thereby assuring circuit
continuity from the other base terminal to electrode 15. The
distal end of side rod 19 is braced to inverted nipple 21 in
tho dome end of the envelope 2 by a clip 22 which engages it.
I have found that a la~p such as illustrated in FIG.
1 wherein the starting gas consist~ of neon with lX argon has
a starting voltage of approximately 300 volts rms in the ab-
sence of any capacitive starting aid. In a preferred em-
bodiment of my invention, I provide a capacitive starting aid
23 consisting of a bifurcated strip of bimetal wrapping around
side rod 19 and spot-welded thereto on opposite sides at 24,
25. The ends of the bimetal are curved at 26, 27 in order to
embrace closely and wrap around the arc tube 9 to achieve good
capacitive coupling thereto. The bimetal strip i8 commercial-
ly available material whereof the low expansion component i8
a nickel-iron alloy and the high expansion component is a
nickel-chrome-steel alloy. Suitable dimen~ions for the bi-
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metal strip material are .005 inch thickne~s by ~150 inch
width. FIGS, 2a and 2b show the starting aid in rest position
at room temperature with the bimetal arms embracing the arc
tube. FIGS. 3a and 3b show the starting aid opened up at op-
erating temperature wherein the arms are swung out and away
from the arc tube as indicated at 26', 27'.
The starting aid illu~trated causes the starting
voltag~ to be reduced from about 300 volts to less than 180
volts. The starting aid is at the potential of the remote
electrode 15 and probably functions by acting a~ a capacitor
in combinatio~ with the proximate electrode 13. A charging
current flows from the starting aid ~hrough the arc tube wall
to the proximate electrode whi~h helps to ignite the lamp.
The magnitude of charging current i~ dependqnt upon the area
of the starting aid in close proximity to the arc tube wall
and hence the need for appreciable width of the bimetal strip
and close conformanco of embrace of the arc tube.
Wh~n the arms of the starting aid ~wing away from
the arc tube, bloskage of light i~ reduced to a 8mall fraction
of that occurring upon engagement and, of cour~e, harmful
overheating of the bimetal material is avoided. R~action
between the starter and the arc tube wall is avoided. Also
thermal etching of the arc tube wall which can occur when
nerqy reflected from the starter raises tho arc tube tempera-
ture ~nough to cause increased vaporization of the ceramic
matQrial~ i8 avoided. Overheating of the arc tube wall can
also occur as ~ result of deflection of the arc toward the
wall by the capacitive effect of the ~tarting aid and this
is aYoid~d when th~ arms swing away from the arc tube.
FIG. 4 illu~tr~te~ another capa¢itive starting aid
30 e~bodying the invention. It comprises a bifurcated and
reverted strip of bimetal wrapping around side rod 19 and
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8pot-welded thoreto on OppOsite sides at 31, 32 The arms
of the ~trip are curved back on them~elves at 33, 34 and re-
directed towards the tube 19 The ends are curved at 35, 36
to wrap around the arc tube to achiev~ good capacitive coupling
thereto. Thi~ construction permits a greater throw of tho
- ends 35, 36 th~n the construction shown in FIGS 2 and 3 It
;, may also be u-ed to accommodate thick r bimetal strip materi-l,
for instance O10U thick material which has le~s flexure for a
givon ¢hange in temperature than the thinn r 005~ thick ma-
,, 10 terial utilizod in FIGS. 2 and 3.
J. Although th capacitive starting aid has been ~hown
a~ op rating in a plano tran~ver~e to the arc tubo axis, that
i i8 not es~-ntial and the arms could be arranged to operate in
a plane including the axis o the arc tube or at any angle
th r-bo
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